The present invention relates to a blast tuyere for shaft furnaces,in particular blast furnaces or hot-blast cupola furnaces.
A typical blast tuyere (denoted xe2x80x9ctuyerexe2x80x9d hereinafter) may include an inner casing and an outer casing which are connected to one another by a nose portion. Hot air is fed through the inner casing while a coolant flows through a hollow space between the inner and outer casings during operation. Tuyeres of this type are water-cooled and mainly made from copper or copper alloys for supply of hot air to the inside of the furnace. When used in connection with blast furnaces, the hot blasts may reach temperatures in the range between 700xc2x0 C. up to more than 1300xc2x0 C. at pressures between 2.5 and 5.5 bar. Hereby, not only the inner casing of the tuyere and in particular the tuyere nose are exposed to severe stress but increasingly also the casing area through melting phases, such as e.g. pig iron, slag, partially reduced burden materials and zinc, and through abrasion with coke and/or wind, as the refractory lining of the furnace progressively wears off to eventually result in an exposure of the tuyere nose. In order to realize a sufficient service life under such severe strains, any tuyere must be intensely cooled by a circulating coolant, normally cooling water, to maintain acceptable temperatures. Moreover, surface wear of the tuyere as a consequence of corroding effect of the melting phases and abrasion should be minimized.
German Offenlegungsschrift DE-OS 35 05 968 describes a tuyere for shaft furnaces, which includes a double-walled hollow body mounted on a base and having an inner casing and an outer casing interconnected by a nose portion. The hollow space formed between the inner and outer casings is divided into an antechamber and a main chamber by an intermediate wall in the area of nose portion. A feed pipe arranged in the base supplies coolant and extends through the main chamber and the intermediate wall to the antechamber. The intermediate wall has several openings so that coolant can flow back from the antechamber to the main chamber and from there via the openings in the base into a ring chamber which is provided with a return flow connection. This conventional tuyere suffers shortcomings because it uses only one cooling circuit. As consequence, when the cooling system breaks down or leaks occur in the tuyere, the coolant amount tapers off, exposing the tuyere to sever stress, which leads in a short time to a destruction of the tuyere and thus to production losses or in a worst case to accidents. In addition, as the cooling water is not guided at various locations, turbulences occur which promote steam bubbles and this greatly impairs the heat dissipation in these locations. In a worst-case scenario, this may lead to localized melting and thus to a destruction of the tuyere.
U.S. Pat. No. 2,735,409 describes a tuyere in which the hollow body is subdivided into an antechamber in the area of the tuyere nose and a main chamber which is connected to the antechamber, wherein the antechamber and the main chamber are completely hydraulically separated from one another and use separate coolant circuits with their own connections. The coolant circuit of the main chamber includes a tightly wound helical pipe which forms the outer casing, whereas the coolant circuit of the antechamber includes two straight pipes arranged in parallel relationship and terminating in a U-shaped ring channel of the tuyere nose. The inner casing may be formed as smooth conical pipe, with both straight pipes of the antechamber disposed between the inner and outer casings, or also as tightly wound helical pipe. The tuyere nose is made as separate member and connected either via anchors with the rear connection piece or directly via a welding seam with the inner and outer casings. This conventional tuyere suffers shortcomings because the configuration dictates that the cooling channels in the main chamber area are very small and of adverse transverse shape (rectangular), and because the configuration dictates that the feed pipe to the antechamber has very small cross sections. In view of the cross sectional reduction and an increasing deviation from a round cross section, the volume stream of coolant decreases superproportionally in the antechamber as well as in the main chamber, resulting in a significant deterioration of the cooling effect. In addition, the cross section of the cooling channel of the antechamber should also be of similarly small size as the cross section of the cooling channel of the main chamber. Thus, the cross section has a rectangular configuration, resulting in very poor side proportions and thus in a poor cooling effect. It is also disadvantageous that the feed channel terminates in the cooling channel of the antechamber, because it leads to a high hydraulic resistance in this cooling circuit, resulting in a smaller volume flow of coolant and lower coolant speed in the antechamber and thus in a poor cooling effect. The overall construction of the tuyere is also very complicated to manufacture and exhibits many critical sealing areas which can to some degree not be remedied. Also the problem of external attack on the main chamber of the tuyere through drop amounts of hot metal in the blast furnace remains unsolved.
It would therefore be desirable and advantageous to provide an improved blast tuyere, which obviates prior art shortcomings and which realizes an effective cooling action of the tuyere nose while being simple in structure and having a long service life and thus being cost-efficient, without substantially altering available coolant amounts and differential pressures.
It would also be desirable and advantageous to provide an improved blast tuyere, which has a geometric configuration sufficient to protect the tuyere from dripping holt melt in the shaft furnace and to provide an effective cooling action also for the main chamber, without substantially altering available coolant amounts and differential pressures and thus operating costs for cooling water.
According to one aspect of the present invention, a blast tuyere for shaft furnaces includes a conical hollow main body defining an upper apex and a lower apex, and having an inner casing, an outer casing and a tuyere nose interconnecting the inner and outer casings, with hot air conducted to the shaft furnace through the inner casing, wherein the outer casing is formed by a single-piece base body having a symmetrical cross section with respect to a vertical axis and terminating in the tuyere nose, without formation of a shoulder, wherein the inner casing is formed by a conical weld-in part; wherein the inner and outer casings define a hollow space through which a coolant stream is conducted during operation and which is subdivided in an antechamber, adjacent the tuyere nose, and a main chamber, which are completely separated hydraulically from one another and include separate coolant circuits, wherein the coolant circuit for the antechamber includes two passages of substantially constant cross section, which are arranged in parallel relationship to the longitudinal axis of the main body and representing a supply flow and a return flow, and which are located in an area of the upper apex of the main body outside a cross section of the main chamber as relating to the longitudinal axis and terminate in a ring channel, which is arranged in the tuyere nose in a direction transversely to the passages, wherein the coolant circuit for the main chamber includes a helical cooling passageway of substantially constant cross section, as viewed in length direction of its extension, with the weld-in part forming an inner wall of the helical cooling passageway of the main chamber, and wherein the passages of the coolant circuit for the antechamber for supply and return of coolant are located in an area of the upper apex of the main body outside an original cross section of the main chamber as relating to the longitudinal axis.
The essence of the invention is the formation of the outer casing by a single-piece base body, which is symmetric with respect to the vertical axis, when viewed in cross section, and has a forward end, which terminates in the front portion without shoulders. The inner casing is formed by a conical weld-in part, which forms the inner wall of the helical cooling channel of the main chamber. A further important feature is the arrangement of channels in 12 o""clock position of the blast tuyere that is relating to the longitudinal axis of the blast tuyere, outside the original cross section of the main chamber, for supply of coolant to the front portion. The proposed arrangement of the cooling channels of the antechamber takes into account the different stress of the blast tuyere, as viewed in circumferential direction. Evidently, the blast tuyere is under more severe stress in 12 o""clock position than in the lateral zones. The intense cooling of this stressed zone significantly increases the service life of the blast tuyere. The coolant circuit of the main chamber may selectively be configured as two-threaded helical cooling channel or provided with one helical cooling channel and a straight cooling channel in 6 o""clock position of the blast tuyere. The straight cooling channel in parallel relationship to the longitudinal axis of the blast tuyere and provided without ribs is arranged in relation to the longitudinal axis of the blast tuyere outside the original cross section of the main chamber of the blast tuyere, with the connections for the supply flow and the return flow disposed adjacent to the connections of the antechamber in the area of the 12 o""clock position. The arrangement of the straight cooling channel in 6 o""clock position of the blast tuyere takes into account the different stress of the blast tuyere in circumferential direction. Apart from the 12 o""clock position, the blast tuyere is also under more severe stress in the 6 o""clock position than in the lateral zones. The intense cooling also in this zone further increases the service life of the blast tuyere.
As already mentioned, the present invention provides to move the supply and return channels for the antechamber as well as the return channel of the main chamber away from the area of the original cross section of the main chamber of the blast tuyere, that is radially outside the main chamber, as relating to the longitudinal axis of the blast tuyere. As a consequence, the cooling channel of the main chamber is free of cross sectional restrictions through provision of supply and return channels. Therefore, optimum conditions for enhancing flow dynamics are attained in the main chamber with greatest possible coolant speeds. Moreover, all stated channels have over the length a substantially constant cross section and the required cross sectional changes in the connection zone as well as the directional changes of small radii are rounded and without irregularities.
These measures implement in the main chamber flow rates for the coolant, which are higher by at least twofold as compared to conventional designs. This is accomplished through elimination of dead zones, swirling regions, throttle areas, backup regions as well as optimum design of the cross sectional configurations of the cooling channels (round, trapezoid) and the cross sectional size of the individual channel portions. The optimum design option of the supply and return channel for the antechamber results also in significantly higher flow rates in the antechamber, without changing the differential pressure. If further implementing a balanced ratio of pumping capacity and channel cross-section to realize the intended high flow rates, bubble formation is substantially suppressed hereby. It is also desired to realize a flow rate of xe2x89xa710 m/sec for the cooling of the highly stressed antechamber and xe2x89xa76 m/sec for the main chamber, when lower differential pressure of, for example, 2 bar is available. The proposed configuration of the blast tuyere is suitable for antechambers with only one ring channel as well as for longer antechambers with a helical channel.
As already mentioned above, the blast tuyere is, however, under stress not only purely thermally, but also additionally chemically and mechanically; in particular when the refractory lining of the shaft furnace is worn-off to a certain degree. Hereby, it is proposed to configure the cross section of the blast tuyere in the area of the 12 o""clock position in a roof-shaped manner. This is advantageous because material falling or dripping on the blast tuyere can slide off or drain easier. This configuration should decrease in particular the undesired contacting of liquid zinc, pig iron or slag with the blast tuyere made of copper or copper alloy. As it is known, zinc reacts with copper so that the copper wall diminishes through chemical degradation.